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Full text of "The Cambridge Natural History"

CHAPTER  XV
RODENTIA-----TILLODONTIA
Order IX.    RODKNTIA1
SMALL to moderately large animals, furry, sometimes with spines.
Toes with nails of a claw-like character, or sometimes approach-
ing hoofs. Usually plantigrade, and only occasionally and
partly carnivorous. Canine teeth absent; incisors long and
strong, growing from persistent pulps, and with enamel only or
chiefly on the anterior face, producing a chisel-shaped edge;
molars few (two to six), separated from the incisors by a wide
diastema. Caecum (nearly always present) very large, and often
complicated in structure. Brain, if not smooth, with few furrows,
the hemispheres not overlapping the cerebellum. Surface of skull
rather flat; orbits not separated from temporal fossae; malar
bone in middle of zygomatic arch; palate very narrow, with
elongated incisive foramina; articular surface for lower jaw
antero-posteriorly elongated. Clavicles generally present. Testes
generally abdominal. Placenta deciduate, and discoidal in form.
The Rodents are a very large assemblage of usually small,
sometimes cjuite minute, creatures, embracing an enormous
number of living generic types. They are distributed all over
the world, including the Australian region, and, being small and
often nocturnal, and by no means particular in their diet, have
managed to thrive and multiply to a greater extent than any
other group of living mammals. They are chiefly terrestrial
creatures, and often burrow or live in ready-made burrows.
1 See especially Tullberg, " tTeber das System der Nagethiere," Act. Ale. Upsala,
1899 ; and Alston, Proe. &&oL Soe. 1875, p. 61; and for nomenclature, Thomas, Proc*
ZooL Soc. 1896, p. 1012 ; and Palmer, Proc. JSiol. Soe. WasJiington, xi. 1897, p. 241.